1) Field of the Invention
The invention relates to a transparent, biaxially oriented polyester film having a base layer of at least 80% by weight based on the total weight of the base layer of at least a thermoplastic polyester, and having a cover layer. The invention furthermore relates to the use of the film and to a process for its production.
2) Prior Art
In many food and drink packaging applications, there is demand for a high barrier effect with respect to gases, water vapor and flavors. For this reason, use is usually made of polypropylene films which are metallized or coated with polyvinylidene chloride (PVDC). However, metallized polypropylene films are not transparent and are therefore not used in cases where the view of the contents is likely to have added promotional effect. Although films coated with PVDC are transparent, the coating, like the metallizing, takes place in a second operation which makes the packaging markedly more expensive. Ethylene-vinyl alcohol copolymers (EVOH) likewise exhibit a strong barrier effect. However, films modified with EVOH are particularly highly sensitive to moisture, and this limits their range of application. In addition, because of their poor mechanical properties they have relatively high thickness or have to be laminated with other materials at high cost, and they are also difficult to dispose of after use. In addition to this, some raw materials are not approved by the authorities or are unsuitable for producing food and drink packaging.
It is therefore an object of the present invention to provide a transparent, biaxially oriented polyester film which can be produced simply and cost-effectively, which has the good physical properties of the known films and which does not give rise to disposal problems.